Disc Cutter for an Earth Boring System

ABSTRACT

In one aspect of the present invention a disc cutter for an earth boring system includes an axle and a sintered polycrystalline ceramic disc disposed about and forming a continuous perimeter around the axle. The disc cutter may be attached to a drill bit comprising a body, working face and plurality of blades. 
     Another aspect of the present invention comprises a method of forming a disc cutter including providing a can of a generally cylindrical shape with a central axis, positioning a column of disposable material, carbide, and crystalline grains in such a manner so when put under high temperature and high pressure a compact in the shape of a disc cutter may be formed and a column from the center axis may be removed. Another method for forming a disc cutter comprises forming a plurality of compacts and bonding the compacts together in a generally toroidal shape.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 12/766,522 which is herein incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

There exists a variety of rock boring machines used to cut through rockformations. Some machines such as the tunnel boring machine (TBM) maycontain disc cutters. Disc cutters are generally rotatable around anaxis and contain a continuous cutting surface. The prior art disclosesrock boring machines containing said disc cutters.

One such disc cutter is disclosed in U.S. Pat. No. 6,131,676 to Friantet al., which is herein incorporated by reference for all that itcontains. Friant et al. discloses small diameter rotary drill bits usingrolling disc cutters. Novel small diameter rotary drill bits withdetachable pedestal mounted rolling disc cutters are provided. The bitbody has a plurality of longitudinal edge mounting slots located atpreselected angularly spaced apart locations. Preferable, the slots eachhave an upper protective ledge and downwardly extending sidewalls. A setof peripheral pedestal mounts each having a mounting portion sized andshaped to fit into a preselected mounting slot are provided and each isdetachably mounted in its preselected mounting slot. In one embodiment,the longitudinally extending slots further comprise a wedge shaped edgeportion, and the pedestal mounts have a complimentary angularly shapedportion, so that when the pedestal mount is brought into a close fittingrelationship with the longitudinal slot, the pedestal mount and thelongitudinal slot are tightly and securely interfitting. The pedestalmounts each include, at the lower reaches thereof, at least one smalldiameter single cutting edge rolling disc cutter. The rolling disccutters are affixed at individually preselected radially spaced apartlocations with respect to a central longitudinal axis forming the centerof rotation of the rotary drill bit. Also, each of the rolling disccutters is mounted at a preselected angle delta with respect to thecentral longitudinal axis forming the center of rotation of the rotarydrill bit. Also, the rolling disc cutters are preferable detachablyaffixed to the pedestal mounts.

Another such disc cutter is disclosed in U.S. Pat. No. 3,981,370 toBingham et al., which is herein incorporated by reference for all thatit contains. Bingham et al. discloses a rock-boring machine of the typecomprising a rotatable headplate having a plurality of disc cuttingunits mounted on the front face of the headplate. Each disc cutting unitincludes an annular rotatable body having a continuous recess extendingaround its periphery and a plurality of cutting segments located in therecess. The segments are secured in the recess by means of removableclamping means.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the present invention a disc cutter for an earth boringsystem comprises an axle and a sintered polycrystalline ceramic discdisposed about and forming a continuous perimeter around the axle.

The sintered polycrystalline ceramic disc may be comprised of a uniformpolycrystalline ceramic material. The disc may contain a carbide coreproximate the axle wherein a sintered polycrystalline ceramic externallayer may be bonded to the carbide core. The carbide core may contain apolycrystalline ceramic interior layer proximate to the axle.

The sintered polycrystalline ceramic disc may contain grooves. Thegrooves may originate from a rim of the disc and terminate at the axleor may be continuous around the axle. The disc may also containprotrusions which extend from and add texture to the ceramic disc.

The sintered polycrystalline ceramic disc may contain two parallelcutting edges comprising supplemental internal angles or two parallelcutting edges each comprising an internal angle greater than 90 degreeswith a rim comprising an internal angle measuring 80 to 140 degrees. Thedistance from at least one cutting edge to the core may be equal to thedistance from the rim to the core.

The disc cutter may contain a plurality of sintered polycrystallineceramic discs.

The axle may include a polycrystalline ceramic layer on its exteriorsurface.

In another aspect of the present invention a drill bit for penetratingearthen formations may include a body comprising of a working face. Theworking face may comprise a plurality of blades converging towards itscenter and diverging toward a gauge of the working face. An axle may bebonded to one of the plurality of blades. A sintered polycrystallineceramic disc may be disposed about and forming a continuous perimeteraround the axle.

The drill bit may also comprise at least one shear cutter disposed onone of the plurality of blades. The axle may be bonded to one of theplurality of blades at the gauge of the working face.

The sintered polycrystalline ceramic disc may be aligned tangent to aperiphery of the working face or may be aligned perpendicular to theworking face.

In another aspect of the present invention a method of forming a disccutter comprises providing a first can which may be of a generallycylindrical shape and contain a central axis, positioning a firstcarbide substrate inside and coaxial with the first can, disposingcrystalline grains inside the first can and forming a continuousperimeter around the first carbide substrate, applying high temperatureand high pressure to the first can to form a first compact, and removinga column from the first compact along the central axis.

The first carbide substrate or the first can may comprise an axiallyhollow region wherein a disposable material may be disposed. Thedisposable material may be comprised of salt, silicon oxide, aluminumoxide, or tungsten carbide.

The column removed from the first compact may be removed by blasting,abrasive lapping, abrasive grinding, or electric discharge machining.

A second can of a generally cylindrical shape and central axis may beprovided and a column of disposable material may be positioned insideand coaxial with the second can. A second carbide substrate comprising atoroidal shape may be positioned inside the second can and encirclingthe second column. Crystalline grains may be disposed inside the secondcan and intermediate to the second carbide substrate and the column ofdisposable material. High temperature and high pressure may be appliedto the second can to form a second compact. The first carbide substrateand the second carbide substrate may then be bonded together.

The first carbide substrate and the second carbide substrate may bebonded together by heating the first compact causing it to expand,depositing the second compact within the first compact, and cooling thefirst compact causing it to shrink onto the second compact.

In another aspect of the present invention a method of forming a disccutter comprises providing a can which may be of a generally cylindricalshape and contain a central axis, positioning a column of disposablematerial along the axis of the can, positioning a carbide substratewhich may be of a toroidal shape coaxial with the can and encircling thecolumn, disposing crystalline grains inside the can and intermediate tothe carbide substrate and column of disposable material, disposingcrystalline grains inside the can and forming a continuous perimeteraround the carbide substrate, applying high temperature and highpressure to the can to form a compact and removing the column from thecompact.

In another aspect of the present invention a method of forming a disccutter includes providing a can, disposing crystalline grains inside thecan, positioning a carbide substrate adjacent to the crystalline grains,and applying high temperature and high pressure to the can to form acompact. The preceding steps may be repeated to form a plurality ofcompacts and wherein the compacts may be bonded together.

The compacts may be bonded together by brazing the carbide substrates ofeach compact. The sintered polycrystalline ceramic external layers ofthe compacts may be flush with each other after brazing. The compactsmay be bonded so that they form a generally cylindrical shape. Thegenerally cylindrical shape may be axially hollow, or a column from thecenter may be removed from the bonded compacts. The column may beremoved by blasting, abrasive lapping, abrasive grinding, or electricdischarge machining.

The can may be of a generally annular sector shape which may be formedby pressing the can around the carbide substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of an embodiment of a drilling operation.

FIG. 2 is a perspective view of an embodiment of a downhole drill bit.

FIG. 3 is a perspective view of an embodiment of a disc cutter.

FIG. 4 a is a cross-sectional view an embodiment of a disc cutter.

FIG. 4 b is a cross-sectional view of another embodiment of a disccutter.

FIG. 5 a is a perspective view of an embodiment of a disc cutter.

FIG. 5 b is a perspective view of another embodiment of a disc cutter.

FIG. 6 a is a perspective view of an embodiment of a disc cutter.

FIG. 6 b is a perspective view of another embodiment of a disc cutter.

FIG. 6 c is a perspective view of another embodiment of a disc cutter.

FIG. 7 is a perspective view of an embodiment of a disc cutter.

FIG. 8 a is a perspective view of an embodiment of a disc cutter.

FIG. 8 b is a perspective view of another embodiment of a disc cutter.

FIG. 9 is a perspective view of an embodiment of a downhole drill bit.

FIG. 10 is a perspective view of an embodiment of a downhole drill bit.

FIG. 11 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 11 b is a flow chart of the steps in a method of forming a disccutter.

FIG. 12 a is a perspective diagram of an embodiment depicting a methodof subjecting a center column to the electrode of an electric dischargemachine (EDM).

FIG. 12 b is a perspective diagram of an embodiment depicting a methodof cutting a center column using an EDM wire.

FIG. 13 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 13 b is a flow chart of the steps in a method of forming a disccutter.

FIG. 14 is a perspective view of an embodiment of a can.

FIG. 15 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 15 b is a flow chart of the steps in a method of forming a disccutter.

FIG. 16 a is a plurality of longitudinal sections representing a methodof bonding two substrates together.

FIG. 16 b is a flow chart of the steps in a method of bonding twosubstrates together.

FIG. 17 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 17 b is a flow chart of the steps in a method of forming a disccutter.

FIG. 18 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 18 b is a flow chart of the steps in a method of forming a disccutter.

FIG. 19 is a perspective view of an embodiment of a can.

FIG. 20 a is a plurality of longitudinal sections representing a methodof bonding two substrates together.

FIG. 20 b is a flow chart of the steps in a method of bonding twosubstrates together.

FIG. 21 a is a plurality of longitudinal sections representing a methodof forming a disc cutter.

FIG. 21 b is a flow chart of the steps in a method of forming a disccutter.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT

Referring now to the figures, FIG. 1 discloses an embodiment of adrilling operation comprising a drilling derrick 101 supporting a drillstring 100 inside a borehole 103. The drill string 100 comprises adrilling assembly 102 with a drill bit 104. The drilling assembly 102may comprise electronic equipment able to send signals through a datacommunication system in the drill string 100 to a computer or datalogging system 106 located at the surface.

FIG. 2 discloses an embodiment of a drill bit 104 comprising a body 201and a working face 202. The working face 202 may comprise a plurality ofblades 203 which may converge towards a center 204 of the working face202 and diverge towards a gauge 205 of the working face 202. The drillbit 104 may comprise a disc cutter 206 comprising a sinteredpolycrystalline ceramic disc 207 disposed about and forming a continuousperimeter around an axle 208. The disc cutter 206 may be disposed in ahole 210 on the drill bit 104 such that the hole 210 may comprisebearing surfaces to slide against the disc cutter 206 and maintain theposition of the disc cutter 206 on the axle 208. In this embodiment, thesintered polycrystalline ceramic disc 207 of the disc cutter 206 isaligned perpendicular to the working face 202.

FIG. 3 discloses an embodiment of a disc cutter 206 containing an axle208 and a sintered polycrystalline ceramic disc 207 which may bedisposed about and the axle 208. The sintered polycrystalline ceramicdisc 207 contains a continuous perimeter 301 around the axle 208 suchthat cutting radius of the disc 207 may be the same as the radius of thedisc cutter 206. In this figure, the sintered polycrystalline ceramicdisc 207 may be composed of a uniform polycrystalline ceramic material.It is believed that the uniformity of the material eliminates weak areasfrom forming in the disc 207. The life of the disc cutter 206 may thusbe extended during normal drilling operations.

FIG. 4 a discloses a cross sectional view of an embodiment of a disccutter 206. The axle 208 acts as a central axis on which the sinteredpolycrystalline ceramic disc 207 can rotate. The axle 208 may comprise apolycrystalline ceramic layer 401 disposed on its exterior surface. Thesintered polycrystalline ceramic disc 207 and the polycrystallineceramic layer 401 may create a plain bearing. The sinteredpolycrystalline ceramic disc 207 and polycrystalline ceramic layer 401may rub against each other without a sealing or lubricant. It isbelieved that this bearing extends the life of the disc cutter 206. Inprior art disc cutters a bearing with a sealing has been necessary dueto the materials used. However, abrasive substances may penetrate thesealing causing the sealing to deteriorate causing the need for the disccutter to be replaced.

Also in FIG. 4 a, the axle 208 may comprise a first stopper 215 and asecond stopper 216. The first stopper 215 may create an increaseddiameter on a portion of the axle 208. The second stopper 216 maycomprise a ring such as a snap ring disposed around the axle 208. Thefirst stopper 215 and the second stopper 216 may comprise bearingsurfaces to slide against the disc cutter 206 and maintain the positionof the disc cutter 206 on the axle 208.

FIG. 4 b discloses a cross sectional view of another embodiment of adisc cutter 206. In this figure, the sintered polycrystalline ceramicdisc 207 may comprise a carbide core 402 proximate the axle 208. Thecarbide core 402 may comprise a polycrystalline ceramic interior layer406 proximate the axle 208. The axle 208 may comprise a polycrystallineceramic layer 401 disposed on its exterior surface. The polycrystallineceramic interior layer 406 of the carbide bore 402 and thepolycrystalline ceramic layer 401 on exterior surface of the axle 208may create a bearing like that described previously.

A sintered polycrystalline ceramic external layer 403 may be bonded tothe carbide core 402. The sintered polycrystalline ceramic externallayer 403 may comprise polycrystalline diamond, synthetic diamond, vapordeposited diamond, silicon bonded diamond, cobalt bonded diamond,thermally stable diamond, polycrystalline diamond with a binderconcentration of 1 to 40 weight percent, infiltrated diamond, layereddiamond, monolithic diamond, polished diamond, course diamond, finediamond, cubic boron nitride, diamond impregnated matrix, diamondimpregnated carbide, silicon carbide, metal catalyzed diamond, orcombinations thereof. It is believed that cubic boron nitride's metallicproperties and heat tolerance make it a particularly effective externallayer in certain formations.

Also in FIG. 4 b, the sintered polycrystalline ceramic disc 207comprises a rim 404 comprising an internal angle 407 measuring 80 to 140degrees located between two parallel cutting edges 405 each comprisingan internal angle 408 greater than 90 degrees. The two parallel cuttingedges 405 may allow for side loading. The two parallel cutting edges 405may be significant because they may increase the cutting area of thedisc cutter 206.

The rim 404 and the two parallel cutting edges 405 can be susceptible tobreaking off during drilling operations. To minimize the likelihood ofbreaking off, the distance 409 from at least one parallel cutting edge405 to the carbide core 402 may be equal to the distance 410 from therim 404 to the carbide core 402.

FIG. 5 a discloses a perspective view of a disc cutter 400. The disccutter 400 may contain a sintered polycrystalline ceramic disc 207comprised of a rim 404 located between two parallel cutting edges 405.

FIG. 5 b discloses an embodiment of a disc cutter 501 containing asintered polycrystalline ceramic disc 502 comprising two parallelcutting edges 503 comprising supplemental internal angles 504. Thisfigure presents a disc cutter 501 which may be valuable in cases whereonly side loading is present.

FIG. 6 a discloses an embodiment of a disc cutter 601 containing grooves604. Grooves 604 may be beneficial in downhole drilling by increasingthe productivity and life of a disc cutter 601. During downholeoperations, occasionally a disc cutter begins to slide along the earthenformation instead of cutting into it. This may put great wear on andcould even break the disc cutter. The grooves 604 in the presentembodiment may act like tread and grip into an earthen formationdisallowing sliding. Grooves 604 can appear in a disc cutter 601 in avariety of patterns. In the embodiment shown, the grooves 604 originateat a rim 605 of the sintered polycrystalline ceramic disc 606 andterminate at an axle 607.

FIG. 6 b discloses another embodiment of a disc cutter 602 containinggrooves 608. In this embodiment the grooves 608 are continuous around anaxle 609.

FIG. 6 c discloses an embodiment of a disc cutter 603 containingprotrusions 610 which may extend from and add texture to a sinteredpolycrystalline ceramic disc 612. The protrusions 610 may increaseproductivity and life of a disc cutter by preventing the disc cutterfrom sliding. Protrusions 610 can appear on a disc cutter in a varietyof patterns. In this figure, the protrusions 610 originate at a rim 611of the sintered polycrystalline ceramic disc 612 and terminate at anaxle 613.

FIG. 7 discloses an embodiment of a disc cutter 701 comprising aplurality of sintered polycrystalline ceramic discs 702 disposed aboutan axle 705. The plurality of discs 702 may increase the cutting area ofthe disc cuter 701. Each disc 702 may be composed of a uniformpolycrystalline ceramic material and comprise a continuous perimeter703.

FIG. 8 a discloses an embodiment of a disc cutter 801. The disc cutter801 comprises a sintered polycrystalline ceramic disc 802 which may bedisposed about and form a continuous perimeter 804 around an axle 803.In this embodiment, the ceramic disc 802 is freely rotatable about theaxle 803.

FIG. 8 b discloses an embodiment of a disc cutter 805. The disc cutter805 comprises a sintered polycrystalline ceramic disc 806 which may bedisposed about and form a continuous perimeter 808 around an axle 807.In this embodiment, the ceramic disc 805 is fixed to the axle 807 suchthat the ceramic disc 805 and the axle 807 rotate together.

FIG. 9 discloses another embodiment of a drill bit 901 comprising a body910 and a working face 905. In the embodiment shown, the drill bit 901contains a disc cutter 902 comprising a sintered polycrystalline ceramicdisc 903 disposed about and forming a continuous perimeter around anaxle 904. The sintered polycrystalline ceramic disk 903 may be alignedtangent to the periphery of the working face 905. The drill bit 901 mayalso contain at least on shear cutter 906 disposed on one of theplurality of blades 907. During the drilling process, the at least oneshear cutter 906 and disc cutter 902 may serve different functions. Thecombination of using both types of cutters may be superior over usingonly one type in certain conditions.

FIG. 10 discloses another embodiment of a drill bit 1001 comprising abody 1010 and a working face 1007. In this figure, the drill bit 1001contains a disc cutter 1002 comprising a sintered polycrystallineceramic disc 1003 disposed about and forming a continuous perimeteraround an axle 1004. The sintered polycrystalline ceramic disc 1003 maybe bonded to one of the plurality of blades 1005 at a gauge 1006 of theworking face 1007. A disc cutter 1002 located in this position mayenlarge the area in which the drill bit 1001 is drilling. Thisembodiment may also include a covering 1015 which may be placed over theaxle 1004. The covering 1015 may prevent the axle 1004 from coming looseduring normal drilling operations. The covering 1015 may comprisebearing surfaces to slide against the disc cutter 1002 and maintain theposition of the disc cutter 1002 on the axle 1004.

FIG. 11 a discloses steps in a method of forming a disc cuttercomprising a sintered polycrystalline ceramic external layer 1108 and acarbide core 1109. A can 1101 comprising a generally cylindrical shapeand a central axis may be provided. A carbide substrate 1102 may bepositioned inside and coaxial with the can 1101. Crystalline grains 1103may be disposed inside the can 1101 and form a continuous perimeteraround the carbide substrate 1102. High temperature 1104 and highpressure 1105 may be applied to the can 1101 to form a compact 1106comprising a sintered polycrystalline ceramic external layer 1108. Acolumn 1107 of carbide substrate 1102 may be removed from the compact1106 along the central axis thus forming a compact 1106 of a generallytoroidal shape. The compact 1106 may be used as a disc cutter comprisinga sintered polycrystalline ceramic external layer 1108 and a carbidecore 1109 with the insertion of an axle.

FIG. 11 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 11 a.

FIG. 12 a discloses a first step of removing the column 1107 from thecompact 1106 along the central axis as described previously. Anelectrode 1201 of an electric discharge machine (EDM) may be plungedinto the carbide substrate 1102 of the compact 1106 forming an initialcavity.

FIG. 12 b discloses a second step of removing the column 1107 from thecompact 1106. After the penetration by the EDM, an EDM wire 1202 may bethreaded through the initial cavity. The EDM wire 1202 may clean theinitial cavity of excess material forming a hollow column in the compact1106.

FIG. 13 a discloses steps in a method of forming a disc cuttercomprising a sintered polycrystalline ceramic external layer 1308 and acarbide core 1309. A can 1301 comprising a generally cylindrical shapeand a central axis may be provided. A column of disposable material 1302may be positioned inside and coaxial with the can 1301. The column ofdisposable material 1302 may comprise salt, silicon oxide, aluminumoxide or tungsten carbide. A carbide substrate 1303 comprising anaxially hollow region may be positioned inside the can 1301 and aroundthe column of disposable material 1302. Crystalline grains 1304 may bedisposed inside the can 1301 and form a continuous perimeter around thecarbide substrate 1303. High temperature 1305 and high pressure 1306 maythen be applied to the can 1301 to form a compact 1307 comprising asintered polycrystalline ceramic external layer 1308. The column ofdisposable material 1302 may then be removed from the compact 1307. Thecompact 1307 may be used as a disc cutter comprising a sinteredpolycrystalline ceramic external layer 1308 and a carbide core 1309 withthe insertion of an axle.

FIG. 13 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 13 a.

FIG. 14 discloses a can 1401 used in a method of forming a disc cutter.The can 1401 comprises a generally cylindrical shape comprising anaxially hollow region 1402. The can 1401 could be used in a methodsimilar to that shown in FIGS. 13 a and 13 b. When high temperature andhigh pressure is applied to the can 1401, a disposable material may bedisposed within the axially hollow region 1402. The disposable materialwould prevent the can 1401 from collapsing inward under the extremeconditions.

FIG. 15 a discloses steps in a method of forming a disc cuttercomprising a polycrystalline ceramic interior layer 1508, carbide core1509, and a sintered polycrystalline ceramic external layer 1510. A can1501 comprising a generally cylindrical shape and a central axis may beprovided. A column of disposable material 1502 may be positioned insideand coaxial with the can 1501. A carbide substrate 1503 comprising atoroidal shape may be positioned coaxial with the can 1501 andencircling the column 1502. Crystalline grains 1504 may be disposedinside the can 1501 intermediate to the carbide substrate 1503 and thecolumn of disposable material 1502. High temperature 1505 and highpressure 1506 may be applied to the can 1501 to form a compact 1507comprising a polycrystalline ceramic interior layer 1508. The column ofdisposable material 1502 may be removed from the compact 1507. Thecarbide substrate 1503 of compact 1507 may be bonded to the carbidesubstrate 1102 of compact 1106. The carbide substrate 1503 and carbidesubstrate 1102 may become the carbide core 1509 when bonded together.The compact 1507 may be used as a disc cutter comprising a sinteredpolycrystalline ceramic external layer 1510 and carbide core 1509 withthe insertion of an axle. A plain bearing may be formed when thepolycrystalline ceramic interior layer 1508 is combined with an axlecomprised of a polycrystalline ceramic exterior surface.

FIG. 15 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 15 a.

FIG. 16 a discloses steps in a method of bonding the carbide substrate1503 of compact 1507 to the carbide substrate 1102 of compact 1106. Heat1601 may be applied to the compact 1106 causing it to expand. Thecompact 1507 may be deposited within the compact 1106. The compact 1106may then be cooled 1602 causing it to shrink. The compact 1106 and thecompact 1507 may be bonded together as the compact 1106 shrinks with thecompact 1507 deposited within it.

FIG. 16 b discloses a flow chart of the steps in a method of bonding twosubstrates together which correspond to the longitudinal sections inFIG. 16 a.

FIG. 17 a discloses steps in a method of forming a disc cuttercomprising a polycrystalline ceramic interior layer 1709, carbide core1710, and a sintered polycrystalline ceramic external layer 1711. A can1701 comprising a generally cylindrical shape and a central axis may beprovided. A column of disposable material 1702 may be positioned insideand coaxial with the can 1701. A carbide substrate 1703 comprising atoroidal shape may be positioned inside and coaxial with the can 1701and encircling the column of disposable material 1702. Crystallinegrains 1704 may be disposed inside the can 1701 and intermediate thecarbide substrate 1703 and column of disposable material 1702.Crystalline grains 1705 may be disposed inside the can and forming acontinuous perimeter around the carbide substrate 1703. High temperature1706 and high pressure 1707 may be applied to the can 1701 forming acompact 1708 comprising a carbide core 1710, and a sinteredpolycrystalline ceramic external layer 1711. The column of disposablematerial 1702 may be removed from the compact 1708. The compact 1708 maybe used as a disc cutter comprising a sintered polycrystalline ceramicexternal layer 1711, carbide core 1710 and polycrystalline ceramicinterior layer 1709 with the insertion of an axle. A plain bearing maybe formed when the polycrystalline ceramic interior layer 1709 iscombined with an axle comprised of a polycrystalline ceramic exteriorsurface.

FIG. 17 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 17 a.

FIG. 18 a discloses a method of forming a disc cutter comprising acarbide core 1808 and a sintered polycrystalline ceramic external layer1809. A can 1800 may be provided. Crystalline grains 1801 may bedisposed inside the can 1800. A carbide substrate 1802 may be positionedinside the can 1800 and adjacent to the crystalline grains 1801. Hightemperature 1803 and high pressure 1804 may be applied to the can 1800forming a compact 1805. The preceding steps may then be repeated forminga plurality of compacts 1805. The plurality of compacts 1805 may bebonded together such that they form an axially hollow generallycylindrical shape 1806 comprising a hollow region 1807. An axle may beinserted into the hollow region 1807 such that a disc cutter comprisinga carbide core 1808 and a sintered polycrystalline ceramic externallayer 1809 carbide core 1808 and a sintered polycrystalline ceramicexternal layer 1809 is formed.

FIG. 18 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 18 a.

FIG. 19 discloses the can 1901 comprising a generally annular sectorshape. The can 1901 may originally be a can 1901 of generallyrectangular shape but may be formed by pressing 1902 the can 1901 aroundthe carbide substrate 1803. The can 1901 comprises a narrow opening 1904such that the carbide substrate 1803 cannot fit through the narrowopening 1904 and fill the volume of the can 1901. The carbide substrate1803 may fit through the opening 1905 of the can 1901 wherein the can1901 may be pressed 1902 together around the carbide substrate 1803. Theshape of the can 1901 allows a plurality of compacts to be bondedtogether in an axially hollow generally cylindrical shape.

FIG. 20 a discloses steps in a method of bonding the carbide substrate2001 of the compact 2002 to the carbide substrate 2003 of the compact2004. A braze metal 2005 may be positioned intermediate the carbidesubstrate 2001 and the carbide substrate 2003. The carbide substrate2001, carbide substrate 2003 and braze metal 2005 may be heated 2010until the braze metal 2005 melts. The melted braze metal 2005 may adhereto both the carbide substrate 2001 and carbide substrate 2003 and may becooled 2011 to become a solid. As the metal braze 2005 is cooled, itacts as a glue between the carbide substrate 2001 and carbide substrate2003 thus bonding them together. The compact 2002 may comprise asintered polycrystalline ceramic external layer 2006 and the compact2004 may comprise a sintered polycrystalline ceramic external layer 2007wherein the ceramic external layer 2006 and ceramic external layer 2007may be flush with each other after brazing.

FIG. 20 b discloses a flow chart of the steps in a method of bondingcarbide substrates together which correspond to the longitudinalsections in FIG. 20 a.

FIG. 21 a discloses a method of forming a disc cutter comprising acarbide core 2108 and a sintered polycrystalline ceramic external layer2109. In this figure, a can 2100 of a generally rectangular shape may beprovided. Crystalline grains 2101 may be disposed inside the can 2100. Acarbide substrate 2102 may be positioned inside the can 2100 andadjacent to the crystalline grains 2101. The can 2100 may be pressed2110 to form a generally triangular shape comprising a curved base. Hightemperature 2103 and high pressure 2104 may be applied to the can 2100forming a compact 2105. The preceding steps may be repeated forming aplurality of compacts 2105. The plurality of compacts 2105 may be bondedtogether such that they form a generally cylindrical shape 2106. Acolumn may be removed from the center of the bonded compacts to form ahollow region 2107. The column may be removed by blasting, abrasivelapping, abrasive grinding, or electric discharge machining. An axle maybe inserted into the hollow region 2107 such that a disc cuttercomprising a carbide core 2108 and a sintered polycrystalline ceramicexternal layer 2109 may be formed.

FIG. 21 b discloses a flow chart of the steps in a method of forming adisc cutter which correspond to the longitudinal sections in FIG. 21 a.

Whereas the present invention has been described in particular relationto the drawings attached hereto, it should be understood that other andfurther modifications apart from those shown or suggested herein, may bemade within the scope and spirit of the present invention.

1. A method of forming a disc cutter, comprising: providing a first cancomprising a generally cylindrical shape and a central axis; positioninga first carbide substrate inside and coaxial with the first can;disposing crystalline grains inside the first can and forming acontinuous perimeter around the first carbide substrate; applying hightemperature and high pressure to the first can to form a first compact;and removing a column from the first compact along the central axis. 2.The method of claim 1, wherein the first carbide substrate comprises anaxially hollow region.
 3. The method of claim 2, wherein a disposablematerial is disposed within the axially hollow region of the firstcarbide substrate.
 4. The method of claim 3, wherein the disposablematerial comprises salt, silicon oxide, aluminum oxide, or tungstencarbide.
 5. The method of claim 1, wherein the first can comprises anaxially hollow region.
 6. The method of claim 5, wherein a disposablematerial is disposed within the axially hollow region of the first can.7. The method of claim 1, wherein removing a column comprises blasting,abrasive lapping, abrasive grinding, or electric discharge machining. 8.The method of claim 1, further comprising: providing a second cancomprising a generally cylindrical shape and a central axis; positioninga column of disposable material inside and coaxial with the second can;positioning a second carbide substrate comprising a toroidal shapecoaxial with the second can and encircling the second column; disposingcrystalline grains inside the second can and intermediate the secondcarbide substrate and the column of disposable material; applying hightemperature and high pressure to the second can to form a secondcompact; and bonding the first carbide substrate to the second carbidesubstrate.
 9. The method of claim 8, wherein the bonding the firstcarbide substrate to the second carbide substrate comprises: heating thefirst compact causing it to expand; depositing the second compact withinthe first compact; and cooling the first compact causing it to shrinkaround the second compact.
 10. A method of forming a disc cutter,comprising: providing a can comprising a generally cylindrical shape anda central axis; positioning a column of disposable material along theaxis of the can; positioning a carbide substrate comprising a toroidalshape coaxial with the can and encircling the column; disposingcrystalline grains inside the can and intermediate the carbide substrateand the column of disposable material; disposing crystalline grainsinside the can and forming a continuous perimeter around the carbidesubstrate; applying high temperature and high pressure to the can toform a compact; and removing the column from the compact.
 11. A methodof forming a disc cutter, comprising: providing a can; disposingcrystalline grains inside the can; positioning a carbide substrateadjacent the crystalline grains; applying high temperature and highpressure to the can to form a compact; repeating the preceding steps toform a plurality of compacts; and bonding the compacts together.
 12. Themethod of claim 11, further comprising removing a column from a centerof the bonded compacts.
 13. The method of claim 12, wherein removing thecolumn comprises blasting, abrasive lapping, abrasive grinding, orelectric discharge machining.
 14. The method of claim 11, wherein thebonding the compacts together comprises bonding the carbide substratesof each compact.
 15. The method of claim 14, wherein the bonding thecompacts together further comprises brazing the carbide substrates ofeach compact.
 16. The method of claim 11, wherein the bonding thecompacts together comprises bonded the compacts such that they form agenerally cylindrical shape.
 17. The method of claim 16, wherein thecylindrical shape is axially hollow.
 18. The method of claim 17, whereinthe compacts each comprise a sintered polycrystalline ceramic externallayer which are flush with each other after brazing.
 19. The method ofclaim 11, wherein the can comprises a generally annular sector shape.20. The method of claim 19, wherein the generally annular sector shapeis formed by pressing the can around the carbide substrate.